Leveraging Model-Based Simulations to Optimize Extended Dosing of Leuprolide 6-Month Intramuscular Depot Formulation

A gonadotropin-releasing hormone (GnRH) agonist such as leuprolide is widely used to achieve sustained suppression of testosterone levels, which play a critical role in the treatment of prostate cancer. Recent advances in drug delivery systems have led to the development of long-acting depot formulations, such as the 6-month intramuscular (IM) leuprolide formulation, which aim to simplify dosing and improve convenience for both patients and healthcare providers. Exploring extended dosing intervals for such formulations represents a promising approach to further optimize treatment regimens, potentially balancing efficacy with patient-centered care. The objective was to evaluate the efficacy of various extended dosing regimens of the leuprolide 6-month IM depot formulation for prostate cancer treatment. The primary objective was to assess whether extended dosing intervals could maintain testosterone concentrations below the castrate threshold of < 0.5 ng/ml and < 0.2 ng/ml in over 90% of subjects, as outlined in regulatory criteria.

The study utilized a previously published pharmacokinetic/pharmacodynamic model to simulate the testosterone suppression profiles for different extended dosing regimens, including every 6 months (Q6M), 7 months (Q7M), 8 months (Q8M), 9 months (Q9M), 10 months (Q10M), 11 months (Q11M), and 12 months (Q12M). The simulations were carried out with 1000 virtual subjects. Sensitivity analyses were also conducted to account for variability in baseline testosterone levels and fraction of drug absorbed.

The simulation results indicated that extending the dosing interval from Q6M to Q8M could ensure that over 90% of subjects maintain testosterone concentrations below 0.2 ng/ml. Similarly, extending the dosing interval to Q9M would keep testosterone concentrations below 0.5 ng/ml in over 90% of subjects. The sensitivity analyses confirmed that these extended dosing regimens consistently achieved and maintained target testosterone levels across various scenarios.

The findings support the feasibility of extending the dosing intervals for the leuprolide 6-month IM depot formulation beyond the label-recommended 6 months. Specifically, the Q8M and Q9M regimens emerged as viable candidates for further clinical evaluation, offering potential benefits in reducing injection frequency while maintaining therapeutic efficacy. Further clinical studies are necessary to confirm the long-term efficacy of these extended dosing regimens.